Typecasting Object to Struct.

[dazibao]

I have a linked list that takes any object, and puts it a struct with some other params:

Let's say:

public VList(Object Data);

passes it to

public struct VData
{
public double ID;
public Object Data;
}

So when you want to retreive it you create a struct, pass it as a ref, and take the struct.data part.

Lets say:

struct Vals
{
public string a;
public string b;
public string c;
public string d;
}

[ creating instances and stuff]

List.Add(vals);

List.Find(id, ref vdata);

vals = (Vals) vdata.Data;

THis actually worked till I changed some code on the list's library (not really had to do with all these).

Now it sends an InvalidCastException like "Specified cast is not valid."

What's wrong with it?

[TheGreatCthulhu]

By the looks of it... everything is wrong with it...
Could you post the code that actually adds the elements to the linked list, so we can have a look?
The exception means that the Data object is not of the Vals type (I'm guessing it's actually a string). It seems to me that you have some misconceptions about what structs are, and how they should be used.

[dazibao]

By the looks of it... everything is wrong with it...
Could you post the code that actually adds the elements to the linked list, so we can have a look?
The exception means that the Data object is not of the Vals type (I'm guessing it's actually a string). It seems to me that you have some misconceptions about what structs are, and how they should be used.

I'm not sure if I get what youre saying. The Data object has been passed a Vals.

Here's the code -if it's the first entry-:

public void Add(Object Data)
{
VData vdata = new VData();
vdata.Data = Data;

if (firstNode == null) //add in empty list
{
vdata.ID = 0;

VNode NVN = new VNode(vdata);

[...]
}

so when you take it back:

public bool Find(double Tid, ref VData data) //extenal use
{
VNode tmp = Search(Tid); //search for the specified id.

if (tmp != null) data = tmp.Data(); //this is the VData struct stored int he node.

else return false;

return true;
}

It actually worked..
I can get for example the ID usinf the vdata.ID, but the vdata.data [which in this case is a Vals structure] do not typecast

[dazibao]

holly ****

Sorry Cthulu, my fault.
Somewhere in one of the node's constr. I missed to pass the obj corectly .
Works fine now

[TheGreatCthulhu]

OK, here's a rough example of how you can implement a linked list in C#.

namespace LinkedListExample
{
    static class Program
    {
        /// <summary>
        /// The main entry point for the application.
        /// </summary>
        [STAThread]
        static void Main()
        {
            Element[] elements = new Element[3];

            for (int i = 0; i < elements.Length; ++i)
            {

                elements[i] = new Element();
                elements[i].Value = "val" + i.ToString();
            }

            MyLinkedList ll = new MyLinkedList();

            foreach (Element e in elements)
                ll.Add(e);

            for (int i = 0; i < ll.Count; ++i)
                Console.WriteLine(ll[i].Value); // prints out: val0, val1, val2            
        }
    }


    public class Element
    {
        public string Value { get; set; }
        public Element Next { get; set; }
    }

    public class MyLinkedList
    {
        private Element head = null;

        public int Count { get; private set; }        

        public void Add(Element item)  // see, no ref keyword required, as long as Element is class, instead of a struct
        {
            if (head == null)
                head = item;
            else
            {
                Element last = head;

                while (last.Next != null)
                    last = last.Next;

                last.Next = item;
            }

            Count++; 
        }

        public Element this[int i]  // indexer
        {
            get
            {
                int k = 0;
                Element current = head;

                while (k < Count)
                {
                    if (i == k)
                        return current;

                    current = current.Next;
                    k++;
                }

                return null;
            }

            // you can implement set...
        }
    }
}